1. Field of the Invention
The present invention relates to a reflector that can be suitably used for a reflection type liquid crystal display device that uses ambient light as a light source. More particularly, the present invention relates to a reflector providing desirable reflectance over a wide angle and a particularly high reflectance in an intended range of directions in which light is reflected, and a reflection type liquid crystal display device providing a wide viewing angle and suitable directionality so that a display surface appears bright within a typical range of viewing angle for a display device incorporated in certain devices such as a notebook personal computer.
2. Description of the Related Art
In recent years, a reflection type liquid crystal display device using ambient light as a light source is widely used as a display part of a handy personal computer and the like particularly because of its low power consumption. A reflection type liquid crystal display device has a reflector which reflects incident light coming through the display surface side back to the display surface side so that the user can view a display that is produced according to the arrangement of liquid crystal molecules in a liquid crystal layer.
When a reflector having a flat surface is used for a reflection type liquid crystal display device, the reflector has high reflectance in a particular reflection angle corresponding to an incident angle. However, the range of reflection angle showing high reflectance is narrow, i.e., the viewing angle is narrow. To solve such a problem, there are several attempts so as to obtain good reflectance in wider range of direction, for example, by forming many concave portions or grooves each being a part of a sphere on a reflector surface, or by providing depressions and projections randomly.
FIG. 15 shows a reflector provided with many concave portions being a part of a sphere on a reflector surface. A reflector 71 shown in this figure is formed as follows. On a substrate 72 made of a glass or the like, a flat-plate resin base material 73 (a base material for a reflector) made of a photosensitive resin layer or the like is provided. On a surface of the base material 72, many concave portions 74 whose inner surfaces being a part of a sphere are formed continuously so as to overlap each other. A reflection film 75 made of a thin film of aluminum, silver or the like is deposited or printed on the concave portions 74.
The concave portions 74 are formed with random depth in a range of 0.1 xcexcm to 3 xcexcm and are arranged randomly with the pitch between adjacent concave portions ranging from 5 xcexcm to 50 xcexcm. An inner surface of each of the concave portions 74 is a curved surface which is a part of a single sphere.
The term xe2x80x9cdepth of a concave portionxe2x80x9d as used herein means the distance from the reflector surface to the bottom of the concave portion, and the term xe2x80x9cpitch of concave portionsxe2x80x9d as used herein means the distance between the center of a concave portion (which has a circular shape as viewed in a plan view) and the center of an adjacent concave portion.
The reflector 71 has a reflection property shown as xcex2 in a comparative example of FIG. 7 or FIG. 12. Each of FIG. 7 and FIG. 12 is a graph showing a reflection property when the incident angle is 30xc2x0, wherein the vertical axis is reflectance (reflection intensity), and the horizontal axis is the reflection angle. The term xe2x80x9cincident anglexe2x80x9d as used herein means an angle xcfx890 between incident light J and a normal line H extending to the surface of the reflector 71 as shown in FIG. 16. Likewise, the term xe2x80x9creflection anglexe2x80x9d as used herein means an angle xcfx89 between the normal line H and reflection light K on a plane including the incident light J and the normal line H. As xcex2 shown in the comparative example of FIG. 7 or FIG. 12, the reflector 71 shows relatively good reflectance, which is in a range of 15xc2x0xe2x89xa6xcfx89xe2x89xa645xc2x0 centered about the reflection angle 30xc2x0.
The conventional reflector 71 described above enables one to obtain relatively good reflectance over a relatively wide angle due to the concave portions. However, as xcex2 shown in the comparative example of FIG. 7 or FIG. 12, the relatively higher reflection intensity peaks at the reflection angles 15xc2x0 and 45xc2x0, which appear symmetrical with the reflection angle 30xc2x0 being an axis of symmetry.
Nevertheless, a display device incorporated in devices such as notebook personal computers, in which a display surface is inclined during its use, is generally viewed from near the direction normal to the display surface as shown in FIG. 17 even though it may vary depending on a degree of inclination of the display surface or a position of the light source. FIG. 17 shows a notebook personal computer having a main body 81 and a cover portion 82, illustrating a situation in which the computer is used. In FIG. 17, P represents a direction normal to a conventional display device 83, Q incident light, xcfx890 an incident angle (e.g., 30xc2x0), R1 reflection light whose reflection angle xcfx89 is the same as the incident angle xcfx890, R2 reflection light whose reflection angle xcfx89 is smaller than the incident angle xcfx890, and R3 reflection light whose reflection angle xcfx89 is greater than the incident angle xcfx890.
As seen in FIG. 17, directions in which a user usually looks at the display device 83 are concentrated in a range of the direction of the reflection light R2 near the normal line P as opposed to a range of the reflection light R3 in which the user has to look up at the display device 83 from a lower direction making it more difficult to see it. Therefore, for convenience of the users, it is desirable to secure a wide viewing angle while enhancing reflectance in the direction in which the reflection angle is smaller than reflection light.
To the contrary, a display device on a horizontal surface such as a table-type game machine is generally looked at from a direction near parallel to the surface as shown in FIG. 18. FIG. 18 shows a display device 85 provided horizontally on a table 84, illustrating a situation in which the device is used. In FIG. 18, W represents a direction normal to the display device 85, S incident light, xcfx890 an incident angle (e.g., 30xc2x0), T1 reflection light whose reflection angle xcfx89 is the same as the incident angle xcfx890, T2 reflection light whose reflection angle xcfx89 is smaller than the incident angle xcfx890, and T3 reflection light whose reflection angle xcfx89 is greater than the incident angle xcfx890.
As seen in FIG. 18, directions in which a user usually looks at the display device 85 are concentrated in a range of the direction of the reflection light T3 whose reflection angle is greater than reflection light T1. Meanwhile, the reflection light T2 is in the range of the direction where a user has to look into the display device, thus making it awkward to see it. Accordingly, for convenience of users, it is desirable to obtain a wide viewing angle and particularly high reflectance in a range of directions in which the reflection angle is greater than the incident angle.
The present invention has been achieved to solve above-described problems. It is therefore an object of present invention to provide a reflector having desirable reflectance over a wide angle, wherein the reflectance can be selectively enhanced in desirable directions such as the reflection angles smaller (including negative values) or greater than the incident angles; and a reflection type liquid crystal display device having a wide viewing angle by incorporating the reflector, and having suitable directionality corresponding to a normal viewing angle under a particular condition such as in cases where the display surface is used inclined, horizontally, or the like.
It is another object of the present invention to provide a reflector having light-diffusing property which suppresses inter-object reflection over a wide angle, and giving particularly high reflectance in an intended range of viewing angle; and to provide a reflection type liquid crystal display device using the same.
To solve above-described problems, the present invention provides a reflector, wherein a plurality of light-reflective concave portions are formed on a surface of a base material; and each of the concave portions is formed so that an inclination angle is maximum on a side portion of the concave surface. The term xe2x80x9cinclination anglexe2x80x9d as used herein means an absolute value of an angle between a plane tangential to a point on the concave surface and the surface of the base material.
The reflector includes a plurality of light-reflective concave portions formed on a surface of a base material. Each of the concave portions is formed in a curved surface (concave surface) so that incident light is basically reflected irregularly, thus having a light diffusing property which suppresses inter-object reflection over a wide viewing angle. Moreover, the concave portions are formed in a curved shape so that an inclination angle is maximum on one side of the concave surface. Accordingly, inclination of a inclined plane opposed to the side of the concave surface becomes relatively gentle, so that the light incident upon the concave portion is reflected so as to have higher luminous density in a direction opposite to the side portion having the maximum inclination angle. Therefore, when the side portion having the maximum inclination angle of each of the concave portions is aligned in one direction, an amount of reflection light can be changed depending upon a viewing angle within a viewing angle range (range of vision).
It is preferable that the concave surface of each of the concave portions has a single minimal point. The term xe2x80x9cminimal pointxe2x80x9d as used herein means a point on a curved surface where an inclination angle is zero, i.e., the deepest point in the vicinity.
The concave portions may be formed in a shape in which, for example, two different spheres each having different curvature overlap. However, there will be two minimal points in this case, so that the reflection angle of light will not change continuously. Then, it may not be possible to obtain the reflection angle that changes smoothly. In order to change the reflection angle of the light smoothly, it is preferable that each of the concave portions has a single minimal point and is formed in non-spherical shape where the maximum inclination angle is inclined on one side.
The inclination angle (an absolute value) is changeable within a range of 2xc2x0 to 80xc2x0. It is particularly preferable within a range of 4xc2x0 to 35xc2x0.
Selection of the inclination angle is preferably changed according to an angle in which an observer views a display surface of a liquid crystal display device, and its range is preferably from 2xc2x0 to 80xc2x0. When it becomes greater than 80xc2x0, the reflection angle on the side surface becomes excessive, so that a part of reflection light exceeds a rim of pixel of a reflection type liquid crystal display device, and therefore, the vision becomes dark. In a case where the inclination angle is less than 2xc2x0, the effect of biasing the viewing angle distribution of an amount of reflection light becomes insufficient, so that it may not be possible to obtain desirable brightness at a particular viewing angle. When applied to electronic appliances such as a desktop calculator or a portable computer in general, the inclination angle (an absolute value) is preferably within a range of 4xc2x0 to 35xc2x0 in view of observers"" normal viewing angle toward the display surface of the liquid crystal display device.
The plurality of concave portions are preferably formed randomly with the depth thereof ranging from 0.1 xcexcm to 3 xcexcm.
When the depth is below 0.1 xcexcm, a light scattering effect is insufficient. When the depth exceeds 3 xcexcm, a base material becomes too thick in order to realize the depth for the concave portions, so that it would be disadvantageous for a manufactured product. By forming the plurality of the concave portions with random depth, generation of moirxc3xa9 pattern resulting from the interference of light can be prevented unlike when the plurality of concave portions are formed with uniform depth. Moreover, concentration of the reflection light amount at a particular viewing angle is diffused so that changes of the reflection light amount within the viewing angle become gradual.
The plurality of the concave portions are preferably arranged adjacently and randomly to each other.
If each of the concave portions is arranged apart from each other, an opening between each of the concave portions becomes a flat surface, thus increasing the flat surface reflection, and therefore, it would become harder to obtain sufficient diffuse reflection within a limited pixel range. Thus, it is preferable that each of the concave portions is arranged adjacent each other. Moreover, if the concave portions were arranged regularly, the moirxc3xa9 pattern would generate. Therefore, it is preferable to arrange them randomly.
The plurality of the concave portions are preferably formed so that the side portion having the maximum inclination angle of the concave surface is aligned in a particular direction.
When the side portion having the maximum inclination angle of the concave surface of each of the concave portions is aligned in the particular direction, an amount of reflection light changes for a whole reflector depending upon the viewing angle. That is to say, in the reflector, an amount of reflection light is a viewing angle dependent. The base material surface appears brighter from a viewing angle for which the display device is designed to give a more reflectance than from other angle. Therefore, a reflection type liquid crystal display device appear to be brighter in an angle from which electronic appliances such as a desktop calculator, a portable computer, and the like are typically viewed.
Moreover, the present invention provides a reflection type liquid crystal display device in which any of the above-described reflectors is mounted. Particularly, the reflector, which preferably has the plurality of the concave portions formed thereon so that the side portion having the maximum inclination angle of the concave surface is aligned in a certain direction, is preferably placed so that the side portion having the maximum inclination angle of each of the concave surfaces is arranged to be a far side from the view point of an observer.
The reflection angle of the concave portions is the largest on the side portion having the maximum inclination angle. Therefore, if a direction of the maximum inclination angle of all of the concave portions is aligned to be a far side from the observer, an amount of reflection light is distributed higher in a direction near the viewpoint of the observer, thus realizing a liquid crystal display device having a bright display surface in a practical view point.
Moreover, in order to solve the above-described problems, the present invention provides a reflector including many concave portions formed on a reflector surface, an inner surface of each of the concave portions including a peripheral curved surface and a bottom curved surface that are continuously connected to each other, the peripheral curved surface being a part of a first sphere having a first radius, the bottom curved surface being a part of a second sphere having a second radius different from the first radius, and the bottom curved surface being located within the peripheral curved surface, wherein the first radius is smaller than the second radius, and a normal line extending from a center of the first sphere to the reflector surface and a normal line extending from a center of the second sphere to the reflector surface are not collinear.
By using the reflector, it is possible to obtain a sufficiently wide viewing angle because a wide range of inclination angle can be obtained due to small radius of the sphere forming the peripheral curved surface. Moreover, the bottom curved surface is a near-flat curved surface in a position slightly off the center of the concave portions, so that the distribution of a particular inclination angle becomes higher in the inner surface of the concave portions. As a result, reflectance becomes its utmost in a reflection angle greater or smaller than an incident angle, and the reflectance becomes higher in the vicinity and peaks at a direction of a such reflection angle.
In this case, the normal lines extending from the respective centers of the spheres to the reflector surface are preferably spaced apart from each other in a range of 0.1 xcexcm to 10 xcexcm. When the interval is less than 0.1 xcexcm, suitable directionality cannot be obtained, and when more than 10 xcexcm, reflection intensity of regular reflection becomes significantly small. The larger the spaced distance of each normal line, the greater a difference between the incident angle and the reflection angle whose reflectance is its highest.
Moreover, an inclination angle of the inner surface of each of the concave portions is desirably in a range of 10xc2x0 to 35xc2x0 and xe2x88x9235xc2x0 to xe2x88x9210xc2x0 for the peripheral curved surface, and in a range of 4xc2x0 to 17xc2x0 and xe2x88x9217xc2x0 to xe2x88x924xc2x0 for the bottom curved surface. The reason is because if the inclination angle of the peripheral curved surface is out of the range of 10xc2x0 to 35xc2x0 and xe2x88x9235xc2x0 to xe2x88x9210xc2x0, the inclination angle of the reflection light becomes too wide so that the reflection intensity decreases. Likewise, when the inclination angle of the bottom curved surface is out of the range of 4xc2x0 to 17xc2x0 and xe2x88x9217xc2x0 to xe2x88x924xc2x0, the reflectance in a particular direction does not become sufficiently high.
In addition, each of the concave portions is desirably formed randomly with depth in a range of 0.1 xcexcm to 3 xcexcm. In a case where the depth is less than 0.1 xcexcm, regular reflection becomes too strong. In a case where the depth exceeds 3 xcexcm, surfaces of convex portions cannot be filled with a smoothing film when concave portions are evened out in a later process, and it becomes impossible to obtain desirable reflection property. If the depth is set to a certain depth for all the concave portions, interference color of light would generate due to regularity, and a problem of coloring of the reflection light would occur.
The term xe2x80x9cdepth of the concave portionsxe2x80x9d as used herein means a distance between the reflector surface and a bottom of the concave portion. Likewise, the term xe2x80x9cinclination angle of the inner surface of the concave portionxe2x80x9d as used herein means an angle xcex8 between horizontal plane and a slope that is defined in a 0.5 xcexcm wide minute area at a position on the inner surface of the concave portion. The sign (positive/negative) of the angle xcex8 is defined with respect to the normal line to the reflector surface. For example, an angle on the right of the normal line is considered positive, and an angle on the left of the normal line is considered negative.
Regarding the arrangement of each of the concave portions, they may be spaced apart from each other but are desirably formed so that they are continuously connected to each other. Accordingly, it is possible to arrange them effectively on a whole surface of the reflector surface, so that the effect of widening a viewing angle while maintaining suitable directionality by the concave portions can be maximized.
Another arrangement is that many concave portions are formed along with many grooves on the reflector surface. Accordingly, in addition to the effect by the concave portions described above, it is possible also to obtain an effect of widening the viewing angle in a direction perpendicular to the grooves by providing the grooves. In this case, the groove can be either straight or curved, and may be crossed each other at any angle. Moreover, the concave portions and the grooves are formed in the density in a range in which effects of each part will not be lost.
Moreover, the present invention provides a reflection type liquid crystal display device having the above-described reflector. The reflector may be either and external type reflector that is provided on the outside liquid crystal cell, or a built-in type reflector that is provided on the inner surface of the substrate of the liquid crystal cell.
The liquid crystal display device of the present invention is provided with a wide viewing angle and suitable directionality. Therefore, when it is incorporated in certain devices such as a notebook personal computer, a game machine and a cellular phone, it is possible to obtain sufficient brightness in the viewing angle which users typically view the device.